The present invention relates to very high areal density magnetic recording media, such as hard disks, which exhibit improved thermal stability, overwrite (OW) capability, and equalized signal-to-media noise ratio (SMNR), and to a method of manufacturing same. More particularly, the present invention relates to a simplified layer structure providing improved longitudinal magnetic recording media utilizing anti-ferromagnetic coupling (AFC) of vertically spaced-apart ferromagnetic layers.
Magnetic recording (xe2x80x9cMRxe2x80x9d) media and devices incorporating same are widely employed in various applications, particularly in the computer industry for data/information storage and retrieval applications, typically in disk form. Conventional thin-film type magnetic media, wherein a fine-grained polycrystalline magnetic alloy layer serves as the active recording layer, are generally classified as xe2x80x9clongitudinalxe2x80x9d or xe2x80x9cperpendicularxe2x80x9d, depending upon the orientation of the magnetic domains of the grains of magnetic material.
A portion of a conventional longitudinal recording, thin-film, hard disk-type magnetic recording medium 1 of single magnetic layer constitution, such as commonly employed in computer-related applications, is schematically illustrated in FIG. 1 in simplified cross-sectional view, and comprises a substantially rigid, non-magnetic metal substrate 10, typically of aluminum (Al) or an aluminum-based alloy, such as an aluminum-magnesium (Alxe2x80x94Mg) alloy, having sequentially deposited or otherwise formed on a surface 10A thereof a plating layer 11, such as of amorphous nickel-phosphorus (Nixe2x80x94P); a seed layer 12A of an amorphous or fine-grained material, e.g., a nickel-aluminum (Nixe2x80x94Al) or chromium-titanium (Crxe2x80x94Ti) alloy; a polycrystalline underlayer 12B, typically of Cr or a Cr-based alloy; a magnetic recording layer 13, e.g., of a cobalt (Co)-based alloy with one or more of platinum (Pt), Cr, boron (B), etc.; a protective overcoat layer 14, typically containing carbon (C), e.g., diamond-like carbon (xe2x80x9cDLCxe2x80x9d); and a lubricant topcoat layer 15, e.g., of a perfluoropolyether. Each of layers 11-14 may be deposited by suitable physical vapor deposition (xe2x80x9cPVDxe2x80x9d) techniques, such as sputtering, and layer 15 is typically deposited by dipping or spraying.
In operation of medium 1, the magnetic layer 13 is locally magnetized by a write transducer, or write xe2x80x9cheadxe2x80x9d, to record and thereby store data/information therein. The write transducer or head creates a highly concentrated magnetic field which alternates direction based on the bits of information to be stored. When the local magnetic field produced by the write transducer is greater than the coercivity of the material of the recording medium layer 13, the grains of the polycrystalline material at that location are magnetized. The grains retain their magnetization after the magnetic field applied thereto by the write transducer is removed. The direction of the magnetization matches the direction of the applied magnetic field. The magnetization of the recording medium layer 13 can subsequently produce an electrical response in a read transducer, or read xe2x80x9cheadxe2x80x9d, allowing the stored information to be read.
Adverting to FIG. 2, a recent approach for improving the microstructure, texture, and crystallographic orientation of magnetic alloys in the fabrication of thin film, high recording density, longitudinal magnetic recording media 1xe2x80x2, involves modification of layer system 12 for microstructure control to include a third or xe2x80x9cinterlayerxe2x80x9d 12C between underlayer 12B and magnetic recording layer 13. A number of Co-based alloy materials, such as CoCr, magnetic CoPtCr, CoPtCrTa, CoCrB, CoCrTa, and CoCrTaOx (where Ox indicates surface-oxidized CoCrTa), etc., have been studied for use as intermediate layers 12C according to such approach, as disclosed in, for example, U.S. Pat. Nos. 5,736,262; 5,922,442; 6,001,447; 6,010,795; 6,143,388; 6,150,016; 6,221,481 B1; and 6,242,086 B1, the entire disclosures of which are incorporated herein by reference.
Magnetic media such as illustrated in FIG. 2 are advantageously fabricated with simultaneous crystallographic orientation and grain size refinement, by interposition of a xe2x80x9cdouble underlayerxe2x80x9d structure (equivalent to a structure represented as 12B1/12B2, wherein 12B1 and 12B2 respectively indicate first-deposited and second-deposited underlayers) between the substrate and the magnetic recording layer, e.g., a Cr/Cr100xe2x88x92xVx or Cr/Cr100xe2x88x92xWx double underlayer structure, with the Cr first underlayer (=12B1) being deposited on the seed layer 12A.
One particular Co-based material suggested for use as interlayer 12C is CO63xe2x88x92xCr37Ptx, where xxe2x89xa68, and a typical layer system 12 including such interlayer may be comprised of a seed layer 12A, e.g., of amorphous or fine-grained Nixe2x80x94Al or Crxe2x80x94Ti, an underlayer 12B, e.g., of a Cr/Cr100xe2x88x92xWx double underlayer structure 12B1/12B2, such as Cr/Cr90W10, and an interlayer 12C, e.g., of CO63xe2x88x92xCr37Ptx, where xxe2x89xa68.
While the above-described seed layer/underlayer/interlayer structures provide improvement in media performance, further efforts are continually being made with the aim of increasing the areal recording density, i.e., the bit density, or bits/unit area, thermal stability, signal-to-medium noise ratio (xe2x80x9cSMNRxe2x80x9d), and other properties/characteristics of high areal density magnetic media. However, severe difficulties are encountered when the bit density of longitudinal media is increased above about 20-50 Gb/in2 in order to form ultra-high recording density media, such as thermal instability, when the necessary reduction in grain size exceeds the superparamagnetic limit. Such thermal instability can, inter alia, cause undesirable decay of the output signal of hard disk drives, and in extreme instances, result in total data loss and collapse of the magnetic bits.
One proposed solution to the problem of thermal instability arising from the very small grain sizes associated with ultra-high recording density magnetic recording media, including that presented by the superparamagnetic limit, is to increase the crystalline anisotropy, thus the squareness of the magnetic bits, in order to compensate for the smaller grain sizes. However, this approach is limited by the field provided by the writing head.
Another proposed solution to the problem of thermal instability of very fine-grained magnetic recording media is to provide stabilization via coupling of the ferromagnetic recording layer with another ferromagnetic layer or an anti-ferromagnetic layer. In this regard, it has been recently proposed (E. N. Abarra et al., IEEE Conference on Magnetics, Toronto, April 2000) to provide a stabilized magnetic recording medium comprised of at least a pair of vertically spaced-apart ferromagnetic layers which are anti-ferromagnetically coupled (xe2x80x9cAFCxe2x80x9d) by means of an interposed thin, non-magnetic spacer layer. The coupling is presumed to increase the effective volume of each of the magnetic grains, thereby increasing their stability. According to this approach, the coupling strength J between the ferromagnetic layer pairs is a key parameter in determining the increase in stability.
Recently, AFC-type, high areal density longitudinal media have been fabricated utilizing a layer system 12 similar to that described supra with respect to conventionally structured high areal density longitudinal media, i.e., comprised, in sequence, of a seed layer 12A, a double underlayer structure 12B1/12B2, and an interlayer 12C, e.g., an amorphous or fine-grained Nixe2x80x94Al or Crxe2x80x94Ti seed layer 12A, a Cr/Cr90W10 double underlayer structure 12B1/12B2, and a CO63Cr37Ptx interlayer 12C, where xxe2x89xa68. Thus, an AFC-type, high areal density magnetic recording medium including such layer system 12 may be described by the following minimum 7-layer structure: non-magnetic substrate//seed layer (xe2x80x9cSDLxe2x80x9d)//2 underlayers (xe2x80x9cULxe2x80x9d)//interlayer (xe2x80x9cILxe2x80x9d)//1st or xe2x80x9cbottomxe2x80x9d magnetic layer (xe2x80x9cBMLxe2x80x9d)//spacer layer for AFC (xe2x80x9cSPLxe2x80x9d)//2nd or recording magnetic layer (xe2x80x9cRMLxe2x80x9d). By way of illustration, an AFC medium comprising such minimum 7-layer structure is: Alxe2x80x94NiP substrate//Nixe2x80x94Al or Crxe2x80x94Ti seed layer//Cr/Cr90W10 double underlayer//Co63xe2x88x92xCr37Ptx interlayer//1st magnetic layer M1//Ru(Cr) spacer layer//2nd magnetic layer M2.
Notwithstanding the improvement in performance of AFC media arising from the enhancements in microstructure, etc. afforded by the above-described seed layer/underlayer/interlayer system, further improvement of AFC media performance (e.g., SMNR) and a reduction in the number of requisite layers, e.g., magnetic layers, leading to increased manufacturing efficiency and cost-effectiveness, are desired.
Accordingly, there exists a need for improved methodology for providing thermally stable, high areal density anti-ferromagnetically coupled (AFC) magnetic recording media, e.g., longitudinal media, with simplified layer structures, i.e., a reduced number of magnetic layers, as well as improved thermal stability and recording characteristics, such as signal-to-media noise ratio (SMNR), overwrite capability (OW), etc., which methodology can be implemented at a manufacturing cost lower than that of conventional manufacturing technologies for forming high areal density AFC-type magnetic recording media comprising a greater number of magnetic layers. There also exists a need for improved, high areal density, AFC-type magnetic recording media, e.g., in disk form, which media include vertically spaced-apart, anti-ferromagnetically coupled ferromagnetic alloy layers separated by a non-magnetic spacer layer, wherein requisite number of magnetic layers is minimized and the media exhibits improved thermal stability and enhanced recording characteristics.
The present invention, therefore, facilitates cost-efficient manufacture of high areal recording density, thermally stable, high SMNR magnetic recording media, e.g., in the form of hard disks, which media utilize anti-ferromagnetic coupling (AFC) between vertically spaced-apart ferromagnetic layers for enhancing thermal stability, while providing full compatibility with all aspects of conventional automated manufacturing technology. Moreover, manufacture and implementation of the present invention can be obtained at a cost comparable to that of existing technology.
An advantage of the present invention is an improved anti-ferromagnetically coupled (xe2x80x9cAFCxe2x80x9d), high areal density magnetic recording medium of simplified thin film layer structure and having improved thermal stability and signal-to-medium noise ratio (xe2x80x9cSMNRxe2x80x9d).
Another advantage of the present invention is a method of manufacturing an improved anti-ferromagnetically coupled (xe2x80x9cAFCxe2x80x9d), high areal density magnetic recording medium of simplified thin film layer structure and having improved thermal stability and signal-to-medium noise ratio (xe2x80x9cSMNRxe2x80x9d).
Additional advantages and other features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized as particularly pointed out in the appended claims.
According to one aspect of the present invention, the foregoing and other advantages are obtained in part by an anti-ferromagnetically coupled (xe2x80x9cAFCxe2x80x9d), high areal density magnetic recording medium of simplified thin film layer structure and having improved thermal stability and signal-to-medium noise ratio (xe2x80x9cSMNRxe2x80x9d), comprising a stack of thin film layers including, in overlying sequence from a surface of a non-magnetic substrate:
(a) a non-magnetic seed layer (xe2x80x9cSDLxe2x80x9d);
(b) at least one non-magnetic underlayer (xe2x80x9cULxe2x80x9d);
(c) a first ferromagnetic layer (xe2x80x9cM1xe2x80x9d);
(d) a non-magnetic spacer layer (xe2x80x9cSPLxe2x80x9d); and
(e) a second ferromagnetic layer serving as a magnetic recording layer (xe2x80x9cM2xe2x80x9d); wherein:
the first ferromagnetic layer (c) serves as a combined interlayer (xe2x80x9cILxe2x80x9d) and xe2x80x9cbottomxe2x80x9d magnetic layer (xe2x80x9cBMLxe2x80x9d) and the non-magnetic spacer layer (d) provides RKKY-type coupling between the first ferromagnetic layer (c) and the second ferromagnetic layer (e) for stabilizing the medium via anti-ferromagnetic coupling (AFC) and improving the SMNR.
According to embodiments of the present invention, the non-magnetic seed layer (a) is from about 10 to about 500 xc3x85 thick and comprises an amorphous or fine-grained material selected from the group consisting of Nixe2x80x94Al, Fexe2x80x94Al, Crxe2x80x94Ti, Crxe2x80x94Ta, Ta, Taxe2x80x94W, Ruxe2x80x94Al, Coxe2x80x94Ti, and Taxe2x80x94N; the at least one non-magnetic underlayer (b) is from about 30 to about 150 xc3x85 thick and comprises a polycrystalline material selected from Cr, Cr alloys, and Cr/Cr100xe2x88x92xMx bi-layer structures, where M is a metal selected from W and V and xxe2x89xa615, e.g., the at least one non-magnetic underlayer (b) is a Cr/Cr90W10 bi-layer structure; the first ferromagnetic layer (c) serving as a combined interlayer and xe2x80x9cbottomxe2x80x9d magnetic layer is from about 30 to about 50 xc3x85 thick and comprises a first CoCrPtB alloy, e.g., a Co68+x+yCr16xe2x88x92xPt8xe2x88x92yB8 alloy, wherein x=0-8 and y=0 or 1, or a CoCrTa alloy, e.g., CoCr14Ta4, and the first ferromagnetic layer (c) has a thickness less than that of the second ferromagnetic layer (e), the thickness of the first ferromagnetic layer (c) being sufficiently small such that at zero external field the magnetic moment thereof points in a direction opposite to the magnetic moment of the second ferromagnetic layer (e); the non-magnetic spacer layer (d) is from about 6 to about 15 xc3x85 thick and comprises a material selected from the group consisting of Ru, Rh, Ir, Cr, Cu, and their alloys, e.g., the non-magnetic spacer layer (d) comprises Ru or a Ruxe2x80x94Cr alloy; the second ferromagnetic layer (e) is from about 100 to about 250 xc3x85 thick and comprises one or more layers of at least one ferromagnetic material selected from alloys of Co with at least one element selected from the group consisting of Pt, Cr, B, Fe, Ta, Ni, Mo, V, Nb, W, Ru, and Ge.
In accordance with further embodiments of the present invention, the magnetic recording medium further comprises:
(f) a third ferromagnetic layer (xe2x80x9cM3xe2x80x9d) between the first ferromagnetic layer (c) and the non-magnetic spacer layer (d) for providing further improvement in equalized SMNR, the third ferromagnetic layer (f) being from about 20 to about 40 xc3x85 thick and comprising a second CoCrPtB alloy, e.g., a Co66+xCr14xe2x88x92xPt10B10, where x=0-8, and the combined thickness of the first ferromagnetic layer (c) and the third ferromagnetic magnetic layer (f) is less than that of the second ferromagnetic layer (e) and sufficiently small such that at zero external field the magnetic moments of both the first ferromagnetic layer (c) and the third ferromagnetic magnetic layer (f) point in a direction opposite to the magnetic moment of the second ferromagnetic layer (e).
According to particular embodiments of the present invention, the non-magnetic substrate comprises a material selected from among Al, Al-based alloys, NiP-plated Al, other metals, other metal alloys, glass, ceramics, polymers, and composites and laminates thereof; the non-magnetic seed layer (a) is from about 10 to about 500 xc3x85 thick and comprises an amorphous or fine-grained material selected from the group consisting of Nixe2x80x94Al, Fexe2x80x94Al, Crxe2x80x94Ti, Crxe2x80x94Ta, Ta, Taxe2x80x94W, Ruxe2x80x94Al, Coxe2x80x94Ti, and Taxe2x80x94N; the at least one non-magnetic underlayer (b) is from about 30 to about 150 xc3x85 thick and comprises a polycrystalline material selected from Cr, Cr alloys, and Cr/Cr100xe2x88x92xMx bi-layer structures, where M is a metal selected from W and V and xxe2x89xa615; the first ferromagnetic layer (c) serving as a combined interlayer and xe2x80x9cbottomxe2x80x9d magnetic layer is from about 30 to about 50 xc3x85 thick and comprises a CO68+x+yCr16xe2x88x92xPt8xe2x88x92yB8 alloy, wherein x=0-8 and y=0 or 1, or CoCr14Ta4; the non-magnetic spacer layer (d) is from about 6 to about 15 xc3x85 thick and comprises a material selected from the group consisting of Ru, Rh, Ir, Cr, Cu, and their alloys; and the second ferromagnetic layer (e) is from about 100 to about 250 xc3x85 thick and comprises one or more layers of at least one ferromagnetic material selected from alloys of Co with at least one element selected from the group consisting of Pt, Cr, B, Fe, Ta, Ni, Mo, V, Nb, W, Ru, and Ge, wherein the first ferromagnetic layer (c) has a thickness sufficiently small such that at zero external field the magnetic moment thereof points in a direction opposite to the magnetic moment of the second ferromagnetic layer (e).
In accordance with further particular embodiments of the present invention, the medium further comprises:
(f) a third ferromagnetic layer (M3) comprising Co66+xCrl4xe2x88x92xPt10B10, where x=0-8, between the first ferromagnetic layer (c) and the non-magnetic spacer layer (d) for providing further improvement in equalized SMNR, the third ferromagnetic layer (f) being from about 20 to about 40 xc3x85 thick, the combined thickness of the first ferromagnetic layer (c) and the third ferromagnetic magnetic layer (f) being less than that of the second ferromagnetic layer (e) and sufficiently small such that at zero external field the magnetic moments of both the first ferromagnetic layer (c) and the third ferromagnetic magnetic layer (f) point in a direction opposite to the magnetic moment of the second ferromagnetic layer (e).
According to another aspect of the present invention, a method of manufacturing an anti-ferromagnetically coupled (xe2x80x9cAFCxe2x80x9d), high areal density magnetic recording medium of simplified thin film layer structure and having improved thermal stability and signal-to-medium noise ratio (xe2x80x9cSMNRxe2x80x9d), comprising the steps of:
(a) providing a non-magnetic substrate including at least one surface; and
(b) forming on the at least one surface a stack of thin film layers comprising, in sequence from the at least one surface:
(i) a non-magnetic seed layer (xe2x80x9cSDLxe2x80x9d);
(ii) at least one non-magnetic underlayer (xe2x80x9cULxe2x80x9d);
(iii) a first ferromagnetic layer (xe2x80x9cM1xe2x80x9d)
(iv) a non-magnetic spacer layer (xe2x80x9cSPLxe2x80x9d); and
(v) a second ferromagnetic layer serving as a magnetic recording layer (xe2x80x9cM2xe2x80x9d);
wherein the first ferromagnetic layer (iii) serves as a combined interlayer (xe2x80x9cILxe2x80x9d) and xe2x80x9cbottomxe2x80x9d magnetic layer (xe2x80x9cBMI,xe2x80x9d), the non-magnetic spacer layer (iv) provides RKKY-type coupling between the first ferromagnetic layer (iii) and the second ferromagnetic layer (v) for stabilizing the medium via anti-ferromagnetic coupling (AFC) and improving the SMNR, and the first ferromagnetic layer (iii) has a thickness less than that of the second ferromagnetic layer (v), the thickness of the first ferromagnetic layer (iii) being sufficiently small such that at zero external field the magnetic moment thereof points in a direction opposite to the magnetic moment of the second ferromagnetic layer (v).
According to certain embodiments of the present invention, step (a) comprises providing a non-magnetic substrate comprising a material selected from among Al, Al-based alloys, NiP-plated Al, other metals, other metal alloys, glass, ceramics, polymers, and composites and laminates thereof; and step (b) comprises forming a stack of thin film layers comprising:
(i) a non-magnetic seed layer from about 10 to about 500 xc3x85 thick and comprised of an amorphous or fine-grained material selected from the group consisting of Nixe2x80x94Al, Fexe2x80x94Al, Crxe2x80x94Ti, Crxe2x80x94Ta, Ta, Taxe2x80x94W, Ruxe2x80x94Al, Coxe2x80x94Ti, and Taxe2x80x94N;
(ii) at least one non-magnetic underlayer from about 30 to about 150 xc3x85 thick and comprised of a polycrystalline material selected from Cr, Cr alloys, and Cr/Cr100xe2x88x92xMx bi-layer structures, where M is a metal selected from W and V and xxe2x89xa615;
(iii) a first ferromagnetic layer from about 30 to about 50 xc3x85 thick, serving as a combined interlayer and xe2x80x9cbottomxe2x80x9d magnetic layer and comprised of a CO68+x+yCrl6xe2x88x92xPt8xe2x88x92yB8 alloy, wherein x=0-8 and y=0 or 1, or CoCr14Ta4;
(iv) a non-magnetic spacer layer from about 6 to about 15 xc3x85 thick and comprised of a material selected from the group consisting of Ru, Rh, Ir, Cr, Cu, and their alloys; and
(v) a second ferromagnetic layer from about 100 to about 250 xc3x85 thick and comprised of one or more layers of at least one ferromagnetic material selected from alloys of Co with at least one element selected from the group consisting of Pt, Cr, B, Fe, Ta, Ni, Mo, V, Nb, W, Ru, and Ge.
According to further embodiments of the present invention, step (b) further comprises forming a third ferromagnetic layer (vi) comprising Co66+xCr14xe2x88x92xPt10B10, where x=0-8, between the first ferromagnetic layer (iii) and the non-magnetic spacer layer (iv) for providing further improvement in equalized SIMR, the third ferromagnetic layer (vi) being from about 20 to about 40 xc3x85 thick, the combined thickness of the first ferromagnetic layer (iii) and the third ferromagnetic magnetic layer (vi) being less than that of the second ferromagnetic layer (v) and sufficiently small such that at zero external field the magnetic moments of both the first ferromagnetic layer (iii) and the third ferromagnetic magnetic layer (vi) point in a direction opposite to the magnetic moment of the second ferromagnetic layer (v).
Yet another aspect of the present invention is an anti-ferromagnetically coupled (xe2x80x9cAFCxe2x80x9d), high areal density magnetic recording medium of simplified thin film layer structure and having improved thermal stability and signal-to-medium noise ratio (xe2x80x9cSMNRxe2x80x9d), comprising:
(a) a non-magnetic substrate; and
(b) means for providing a combined interlayer and bottom magnetic layer for a pair of anti-ferromagnetically coupled ferromagnetic layers.
Additional advantages and aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the present invention are shown and described, simply by way of illustration of the best mode contemplated for practicing the present invention. As will be described, the present invention is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects, all without departing from the spirit of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as limitative.